1. Field of the Invention
The present invention relates to a wireless power supply technique.
2. Description of the Related Art
In recent years, in order to supply electric power to an electronic device, contactless power transmission (which is also referred to as “contactless power supply” or “wireless power supply”) has begun to come into commonplace use. In order to advance the compatibility of products between manufacturers, the WPC (Wireless Power Consortium) has been organized, and the WPC has developed the Qi standard as an international standard.
FIG. 1 is a diagram showing a configuration of a wireless power supply system 100 that conforms to the Qi standard. The power supply system 100 includes a power transmission apparatus 200 (TX, Power Transmitter) and a power receiving apparatus 300 (RX, Power Receiver). The power receiving apparatus 300 is mounted on an electronic device, examples of which include cellular phone terminals, smartphones, audio players, game machines, and tablet terminals.
The power transmission apparatus 200 includes a transmission coil (primary coil) 202, a driver 204, a controller 206, and a demodulator 208. The driver 204 includes an H-bridge circuit (full-bridge) circuit or otherwise a half-bridge circuit. The driver 204 applies a driving signal S1 in the form of a pulse signal to the transmission coil 202 such that a driving current flows through the transmission coil 202, thereby generating an electric power signal S2 in the form of an electromagnetic signal. The controller 206 integrally controls the overall operation of the power transmission apparatus 200. Specifically, the controller 206 controls the switching frequency of the driver 204 or otherwise the duty ratio of the switching of the driver 204 so as to adjust the electric power to be transmitted.
In the Qi standard, a protocol is defined for communication between the power transmission apparatus 200 and the power receiving apparatus 300, which enables information transmission from the power receiving apparatus 300 to the power transmission apparatus 200 via a control signal S3. The control signal S3 is transmitted from a reception coil 302 (secondary coil) to the transmission coil 202 in the form of an AM (Amplitude Modulation) modulated signal using backscatter modulation. The control signal S3 includes electric power control data (which will also be referred to as a “packet”) which indicates an amount of electric power to be supplied to the power receiving apparatus 300, and data which indicates the particular information for identifying the power receiving apparatus 300. The demodulator 208 demodulates the control signal S3 included in the current or otherwise the voltage applied to the transmission coil 202. The controller 206 controls the driver 204 based on the power control data included in the control signal S3 thus demodulated.
The power receiving apparatus 300 includes the reception coil 302, a rectifier circuit 304, a capacitor 306, a modulator 308, a load circuit 310, a controller 312, and a power supply circuit 314. The reception coil 302 receives the electric power signal S2 from the transmission coil 202, and transmits the control signal S3 to the transmission coil 202. The rectifier circuit 304 and the capacitor 306 rectify and smooth a current S4 induced at the reception coil 302 according to the electric power signal S2, thereby converting the current S4 into a DC voltage.
Using electric power supplied from the power transmission apparatus 200, the power supply circuit 314 charges an unshown secondary battery or steps up or otherwise step down the DC voltage Vdc, so as to supply the DC voltage to the controller 312 and other load circuits 310.
The controller 312 monitors the amount of electric power supplied to the power receiving apparatus 300, and accordingly generates electric power control data which indicates the amount of power transmission. The modulator 308 modulates the control signal S3 including the electric power control data so as to modulate the coil current that flows through the reception coil 302, thereby modulating the coil current and coil voltage applied to the transmission coil 202.
The above is the configuration of the power supply system 100. FIG. 2 is a flowchart showing an operation sequence of the power transmission apparatus 200. The states of the power transmission apparatus 200 can be roughly classified into three phases, i.e., a selection phase ϕ1, a power transfer phase ϕ2, and an identification and configuration phase ϕ3.
First, description will be made regarding the power transfer phase ϕ2. The power transmission apparatus 200 (TX) starts to supply electric power to the power receiving apparatus 300 (RX) (S100). The power transmission apparatus TX receives the control signal S3 from the power receiving apparatus RX as a feedback signal which indicates the current power transmission state (S102). The power transmission apparatus TX adjusts the amount of power transmission based on the control signal S3 (S104).
When the power transmission apparatus TX receives, from the power receiving apparatus RX, the control signal S3 indicating that charging is complete (S106), or otherwise detects, based on a communication timeout error, that the power receiving apparatus RX has been removed from the area where it can receive electric power from the power transmission apparatus TX (S108), the power transmission apparatus TX stops the power transmission, and enters the selection phase ϕ1.
Next, description will be made regarding the selection phase ϕ1. The power transmission apparatus TX transmits the electric power signal S2 at a predetermined time interval (object detection interval, e.g., every 500 msec), so as to check for the presence or absence of the power receiving apparatus RX (S200). This phase will be referred to as the “analog ping phase”.
When the power receiving apparatus RX is detected (S202), the power transmission apparatus TX transits to the identification and configuration phase ϕ3, and a digital ping phase is executed (S204). Subsequently, in the identification and configuration phase ϕ3, the power transmission apparatus TX receives identification information for the power receiving apparatus RX (S206). Subsequently, the power receiving apparatus RX transmits the information with respect to the power transmission conditions to the power transmission apparatus TX (S208). In this stage, the power transmission apparatus TX transits to the power transfer phase ϕ2. The above is the operation sequence of the power transmission apparatus 200.